All available evidence supports the central conclusions of evolutionary
theory, that life on Earth has evolved and that species share common
ancestors. Biologists are not arguing about these conclusions. But they
are trying to figure out how evolution happens, and that's
not an easy job. It involves collecting data, proposing hypotheses, creating
models, and evaluating other scientists' work. These are all activities
that we can, and should, hold up to our checklist and ask the question:
are they doing science?

All sciences ask questions about the
natural world, propose explanations in terms of natural processes, and
evaluate these explanations using evidence from the natural world.
Evolutionary biology is no exception. Darwin's basic conception of
evolutionary change and diversification (illustrated with a page from his
notebook at left) explains many observations in terms of natural processes and
is supported by evidence from the natural world.

Some of the questions that evolutionary biologists are trying to answer
include:

Does evolution tend to proceed slowly and steadily or in quick jumps?

Why are some clades very diverse and some unusually sparse?

How does evolution produce new and complex features?

Are there trends in evolution, and if so, what processes generate them?